Being obese or even overweight may boosts a person’s risk of developing up to a dozen different types of cancers, a European research analysis shows.

It is already known that obesity is a major issue worldwide and raises the risk of diseases such as type 2 diabetes and heart problems. According to the World Health Organization, there are 400 million people classified as obese and 7.6 million people died last year, worldwide, because of cancer, the American Cancer Society reported.

Researchers at the University of Manchester, northwestern England, analyzed data from 141 studies that monitored the health of 282,000 people from Europe, North America, Asia, and Australia who experienced weight gain at some point of the study.

The benchmark of fat was the body mass index (BMI), in which the individual’s weight in kilos is divided by the square of the person’s height in meters. Individuals with a BMI of 25-29.9 are considered overweight, while those with a BMI of 30 or more are obese.

The subjects were followed for about nine to 15 years, with researchers tracking their BMI and correlating it with incidents of cancer.

The researchers found that being obese influenced the chances of developing cancer differently in men and women. In men, an average gain of 33 pounds increased the risk of esophageal cancer by 52 percent, thyroid cancer by 33 percent, and colon and kidney cancers each by 24 percent. In women, a weight gain of 29 pounds increased the risk of cancer in the uterus and gall bladder by nearly 60 percent, esophagus by 51 percent and kidney by 34 percent, the study said.

“Increased BMI is associated with increased risk of common and less common malignancies. For some cancer types, associations differed between sexes and populations of different ethnic origins,” said Andrew Renehan, a cancer specialist at the University of Manchester, who led the study.

The chances of men with a higher BMI developing rectal cancer and malignant melanoma also rose, as did the risk of women getting post-menopausal breast, pancreatic, thyroid, and colon cancers. The risk of leukemia, non-Hodgkin’s lymphoma, and multiple myeloma rose in both sexes. The research also found that the association between increased BMI and breast cancer in Asia-Pacific populations was stronger than in any other ethnic group.

“The number of deaths per year attributable to obesity is about 30,000 in the UK and 10 times that in the USA, where obesity has been estimated to have overtaken smoking in 2005 as the main preventable cause of illness and premature death. Efforts will be needed to increase education on diet and physical activity,” epidemiologist Dr. Susanna Larson and Professor Alicja Wolk said commenting on the study.

Scientists do not know for sure how being overweight could make people more susceptible to cancer.

“One of the hypotheses is that the presence of excess fat cells could affect the levels of hormones in your body. At a cellular level, that may favor the development of tumors in humans,” Renehan said.

However, Dr. Renehan said there is no definitive proof that being fat itself causes cancer.

“To make the link between cause and effect, we need to tick several boxes. This study begins to tick the first two or three boxes, but more research is needed to confirm it,” Renehan said.

Whether or not being obese increases the risk of developing different types of cancer, one thing is for sure. Losing weight is of great help in preventing people getting in trouble.

“The simple message is that, if you manage to keep a healthy body weight, you will have a lower risk of developing cancer,” said Ed Yong, of Cancer Research United Kingdom quoted by the Associated Press.

But how can people lose weight when “there are many, many things in our social and physical environmental that make it easy to gain weight,” American Cancer Society epidemiologist Michael Thun, MD, MS, said. “Food is everywhere, and physical activity is no longer built into our daily lives. For most people it is voluntary. They know that obesity is linked to heart disease and diabetes. But the average person on the street would still be surprised that obesity is related to cancer risk.”

The findings are published Friday in the journal Lancet.